A new study claims that the ancient winged reptiles known as pterosaurs used a "pole-vaulting" action to take to the air.
They say the creatures took off using all four of their limbs.
The reptiles vaulted over their wings, pushing off first with their hind limbs and then thrusting themselves upwards with their powerful arm muscles - not dissimilar to some modern bats.
The research is published in the open-access journal Plos One.
Pterosaurs lived at the same time as the dinosaurs, but belonged to a different group of reptiles. They existed from the Triassic Period until the end of the Cretaceous - about 220 million years ago to 65 million years ago.
In their study, Dr Mark Witton at Portsmouth University, UK, and Dr Michael Habib of Chatham University, Pennsylvania, US, reappraised giant pterosaur fossils.
Their findings challenge other claims that the giant pterosaurs - such as Pteranodon and the largest azhdarchids - were not capable of flying.
Researchers have previously suggested that these creatures were too heavy to have taken to the skies.
There have also been doubts that the ancient reptiles could have taken off using the same action as birds.
"Most birds take off either by running to pick up speed and jumping into the air before flapping wildly, or if they're small enough, they may simply launch themselves into the air from a standstill," said Dr Witton.
"Previous theories suggested that giant pterosaurs were too big and heavy to perform either of these manoeuvres."
He added: "These creatures were not birds; they were flying reptiles with a distinctly different skeletal structure, wing proportions and muscle mass.
"They would have achieved flight in a completely different way to birds and would have had a lower angle of take off and initial flight trajectory."
The authors of the latest study suggest that, with up to 50kg of forelimb muscle, the creatures could easily have launched themselves into the air despite their massive size and weight.
Dr Habib explained: "Instead of taking off with their legs alone, like birds, pterosaurs probably took off using all four of their limbs.
"By using their arms as the main engines for launching instead of their legs, they use the flight muscles - the strongest in their bodies - to take off and that gives them potential to launch much greater weight into the air," he explained.
"When they were far enough off the ground, they could start flapping their wings before finding a thermal or another area of uplift to gain some altitude and glide off to wherever they wanted to go," he told BBC News.
The largest pterosaurs may have had wingspans up to 13m and weighed up to 544kg.
But the authors' reappraisal of pterosaur fossils suggests these numbers may have been overestimated. They argue that the biggest creatures may have had 10-11m wingspans and weighed between 200 and 250 kg.